Scintillation camera and sensor for use therein

ABSTRACT

A scintillation camera having a detector with a surface and designed to form a tomographic image of a subject from radiation emitted from radio isotope administered to the subject and detected by the detector. The camera comprises a data acquiring device for acquiring data required to reconstruct a tomographic image of the subject, and a detector holder for holding the detector at a predetermined distance from the body surface of the subject while the data acquiring device is acquiring the data. The detector holder includes a sensor located between the subject and the detection surface of the detector, a sensor control circuit for controlling the sensor and detecting ON/OFF state of the sensor, and a detector moving device for moving the detector toward and away from the subject in accordance with the ON/OFF state detected by the sensor control circuit.

This application is a Continuation of application Ser. No. 08/845,239,filed on Apr. 21, 1997, which is a Continuation of application Ser. No.08/142,050, filed Oct. 28, 1993 (now U.S. Pat. No. 5,625,191).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a scintillation camera, moreparticularly to the scanning of a subject by means of a detectorincorporated in the scintillation camera, and to a non-contact typesensor for use in a nuclear medicine diagnostic apparatus or in an X-raydiagnostic apparatus.

2. Description of the Related Art

A scintillation camera is used to form a functional image of a livingsubject while a detector is scanning the subject and detecting thegamma-rays emitted from the radioisotope labeled with a specificmedicine administered to the subject.

The camera serves to determine, from the gamma-rays detected, thedistribution of the radioisotope within the subject, in order to therebyvisualize the shape and functional condition of an organ, the presenceor absence of a lesion, and metabolic function of the subject. Althoughit has a low resolution and involves radiation exposure of the subject,it is used in specific fields such as the early detection of a brainischemia section and estimation of the viability of myocardial cells.The scintillation camera serves as an apparatus which assists an X-raycomputed tomography apparatus.

A conventional scintillation camera is operated to scan to obtain aSPECT (Single Photon Emission Computed Tomographic) image of a subjectby one of the following two alternative methods.

The first method, generally known as "4-point determination method,"serves to input four points before the detector of the camera is movedaround a subject to scan the subject. Of these points, two are on amajor axis extending in the width direction of the subject, and theother two are on a minor axis extending in the thickness direction ofthe subject. That is, an appropriate distance from the center ofrotation along the turning radius is input every time the detector isrotated by 90°, thereby calculating an arc for each quadrant. Thedetector is thereby moved in an elliptical orbit passing the fourpoints.

The second method is to rotate the detector once around the subject inan elliptical orbit, before the acquisition of data from the subject,thereby obtaining data representing the elliptical orbit. Then, thedetector is moved around the subject along the elliptical orbitrepresented by the data, to scan the subject.

In the first method, data items representing the four points must beinput to define an elliptical orbit, prior to the scanning of thesubject. In the second method, the detector must be moved once aroundthe subject in an elliptical orbit to acquire the data representing thisorbit, prior to the scanning of the subject. In either method it isnecessary to set an orbit for the detector before the acquisition ofdata from the subject. Furthermore, the subject may move after the orbithas been set, making it necessary to adjust the orbit. However, theorbit can hardly be adjusted once it has been thus set or once the dataacquisition has been started.

Particularly, in the 4-point determination method, the orbit for thedetector is an elliptical one which has not been set on the basis of theoutline of a transverse section of the subject. The orbit is not anideal orbit which should preferably closely surround the subject.

As indicated above, the conventional scintillation camera cannot be usedbefore an orbit is set for the detector or the data representing such anorbit is input. The subject may move, making it necessary to adjust theorbit. However, it is difficult to adjust the orbit once the orbit hasbeen set or once the data acquisition has been initiated. Further, inthe 4-point determination method it is impossible to set an ideal orbitclosely surrounding the subject.

A scintillation camera of so-called "whole body type," is known, whichscans a subject while its detector is moving along the body axis of thesubject. The conventional whole body-type scintillation camera isoperated to scan a subject by one of the following three alternativemethods.

In the first method, as shown in FIG. 1A, the detector 48 is located ata position which has been determined based on the highest point of theridge line showing the lateral section of the subject 50 lying on thebed (hereinafter, referred to as only a subject for simplicity in somecases). Then, the detector 48 is moved along the body axis of thesubject 50, while maintained at that position, to thereby scan the wholebody of the subject 50.

In the second method, as shown in FIG. 1B, the detector 48 is movedalong the ridge line of the subject 50, prior to the scanning of thesubject 50, thereby obtaining data representing the curved path of thedetector 48. Then, the detector 48 is automatically moved along thecurved path represented by the data thus obtained, to thereby scan thewhole body of the subject 50.

In the third method, the detector is located at a scanning startposition, a scanning length, or a scanning end position, is determinedon the basis of the height of a subject and input, and the detector ismoved from the scanning start position to the scanning end position.While being so moved, the detector acquires whole-body data from thesubject.

The three methods have problems, however.

The first method is problematic in two respects. First, it takes manytimes to determine a proper position for the detector 48. Second, thedetector 48 is positioned too far a distance away from the subject 50,except for a moment it is located close to the highest point on theridge line. The resolution of the scintillation camera is thereforedecreased.

The second method is problematic in two respects, too. First, it takestoo much time to obtain the data showing the curving path of thedetector 48. Second, data acquisition from the subject 50 is interruptedwhen the subject 50 moves, inadvertently touching the detector 48, asoften happens, while the detector 48 is moving along the curving path.

The third method is problematic in two respects, too. First, an operatormust take pains to locate the detector at a scanning start positionwhere the head or toes of the subject is completely within the viewfield of the detector, while looking at the image picked up by thedetector. Inevitably it takes a long time to locate the detector at adesirable scanning start position. Second, it is necessary for theoperator to determine the scanning length, or the scanning end position,on the basis the height of the subject, and to input the scanninglength. To determine and input the scanning length is alsotime-consuming.

Scintillation cameras are used, each in combination with one sensor.

The sensor comprises a plurality of light-emitting elements and aplurality of light-receiving elements, which are arranged in the sameplane. The light-receiving elements oppose the light-emitting elements,respectively, spaced apart therefrom by a predetermined distance. Thesensor is designed for industrial use. When all light-receiving elementsreceive light from the associated light-emitting elements, it isdetermined that no object lies between the light-emitting elements onthe one hand, and the light-receiving elements on the other hand. Whenany one of the light-receiving elements does not receive light from theassociated light-emitting element, it is determined that an object liesbetween the light-emitting elements and the light-receiving elements.

FIG. 2 schematically shows a conventional sensor of this type.

As shown in FIG. 2, a plurality of light-emitting elements 11₁ to 11_(N)and a plurality of the light-receiving elements 12₁ to 12_(N) arearranged in the same plane. The elements 12₁ to 12_(N) oppose thelight-emitting elements 11₁ to 11_(N), respectively, spaced aparttherefrom by a predetermined distance. Each light-receiving element 12receives the light emitted from the associated light-emitting element11. The optical axis extending between each light-emitting element 11and the associated light-receiving element 12, shown by a broken line,is parallel to the optical axis extending between any other associatedelements 11 and 12. When an object 50 exists between the light-emittingelements 11 on the one hand and the light-receiving elements 12 on theother hand, at least one of the light-receiving elements 12 cannotreceive the light emitted by the associated light-emitting element 11.Thus, the presence or absence of an object can be determined from thesignals output by the light-receiving elements 12. The light-emittingelements 11 and the light-receiving elements 12 are controlled by asensor controller 20. The controller 20 generates a signal representingthe presence or absence of an object. This signal is used for variouspurposes. The plane in which the elements 11 and 12 are arranged iseither horizontal or vertical, in accordance with the purpose for whichthe sensor is employed.

The sensor for industrial use, shown in FIGS. 3A and 3B, may make errorswhen a light-reflecting object is located in the vicinity of thelight-emitting elements 11 and the light-receiving elements 12.

As shown in FIG. 3A, a light-reflecting flat object may be located nearthe light-emitting elements 11 and the light-receiving elements 12. Inthis case, the light emitted from any light-emitting element 11 isreflected or scattered on the reflecting surface of the object and isthen applied to the light-receiving element 12 associated with thelight-emitting element 11.

As shown in FIG. 3B, the sensor may be located near a light-reflectingwall or floor. In this case, too, the light emitted from anylight-emiting element 11 is reflected or scattered on the reflectingsurface of the object and is then applied to the light-receiving element12, associated with the light-emitting element 11.

In either case, the sensor outputs a signal representing the absence ofan object, despite the fact that there is an object located between thelight-emitting element 11 and the light-receiving element 12.

A sensor of the type shown in FIG. 2 is often used in combination withthe medical scintillation camera described above, with itslight-emitting elements 11 attached to one end of the camera, and itslight-receiving elements 12 secured to the other end of the camera. Thescintillation camera, which is a reflector, extends parallel to theoptical axis of the sensor. The light reflected from and scattered bythe scintillation camera adversely affects the reliability of thesensor. When the sensor makes an error due to the reflected or scatteredlight, the camera may abut on a subject or may be stopped.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a scintillation camerawhich can easily acquire data required for reconstructing a tomographicimage of a subject, without the necessity of setting an orbit for adetector prior to the acquisition of data, which has an enhanced imageresolution, which can effectively acquire data regardless of thesubject's body shape, and which can continue to acquire data even if thesubject moves during the data acquisition.

In a first aspect of the present invention, there is provided ascintillation camera having a detector with a detector surface anddesigned to form a tomographic image of a subject from radiation emittedfrom radioisotope administered to the subject and detected by thedetector. The camera comprises: data acquiring means for acquiring datarequired to reconstruct a tomographic image of the subject; and detectorholding means for holding the detector at a predetermined distance fromthe body surface of the subject while the data acquiring means isacquiring the data.

The scintillation camera is characterized in that the detector holdingmeans includes: a sensor located between the subject and the detectionsurface of the detector; a sensor control circuit for controlling thesensor and detecting ON/OFF state of the sensor; and detector movingmeans for moving the detector toward and away from the subject inaccordance with the ON/OFF state detected by the sensor control circuit.

As indicated, the detector holding means holds the detector at apredetermined distance from the subject during the data acquisition.Therefore, an orbit in which the detector is to rotate around thesubject need not be set prior to the data acquisition, by inputting fourpoints as in the 4-point determination method. Nor is it necessary toinput data showing the orbit into the scintillation camera prior to thedata acquisition. Hence, the preparation time for data acquisition canbe shortened.

Since the detector holding means holds the detector at a predetermineddistance from the subject throughout the data acquisition, the dataacquisition need not be interrupted at all even if the subject moveswhile being scanned. For the same reason, the detector rotates in anoptimal orbit around the subject, however shaped the subject is.

Moreover, accurate data representing the ridge line of the subject canbe recorded from the orbit in which the detector has been rotated aroundthe subject and can be utilized as absorption-correcting data in orderto reconstruct a tomographic image of the subject.

In a second aspect of the invention, there is provided a scintillationcamera having a detector with a detector surface and designed to obtaina distribution of the radiation emitted from radioisotope administeredto the subject and detected by the detector while the detector is beingmoved relative to the subject along a body axis of the subject. Thiscamera comprises: data acquiring means for acquiring data from thesubject; and detector holding means for holding the detector at apredetermined distance from the body surface of the subject while thedata acquiring means is acquiring the data.

The scintillation camera is characterized in that the detector holdingmeans includes: a sensor located between the subject and the detectionsurface of the detector; a sensor control circuit for controlling thesensor and detecting ON/OFF state of the sensor; and detector movingmeans for moving the detector toward and away from the subject inaccordance with the ON/OFF state detected by the sensor control circuit.

With this scintillation camera it is possible to determine whether thedetector has approached the subject or retreated therefrom excessively,and to move the detector toward or away from the subject in accordancewith the position of the detector, thereby to maintain the detector at adesired distance from the subject throughout the data acquisition.Hence, it is unnecessary to collect data before the data acquisition inorder to set an optimal orbit for the detector. Furthermore, thedetector can be positioned close to the subject while rotating aroundthe subject even if the subject moves during the data acquisition. Thisserves to enhance the image resolution of the scintillation camera.

Another object of the present invention is to provide a scintillationcamera in which the detector is automatically positioned, moved andstopped.

In a third aspect of the invention, there is provided a scintillationcamera having a detector with a detector surface and designed to acquiredata from a subject by detecting radiation emitted from radioisotopeadministered to the subject while the detector is being moved relativeto the subject along a body axis of the subject. This scintillationcamera comprises: drive means for moving the detector relative to thesubject along the body axis of the subject; a sensor connected to thedetector, for detecting a position of the subject with respect to thedetector and for outputting a signal representing the position of thesubject; and control means for controlling the drive means in accordancewith the signal output from the sensor.

In the scintillation camera according to the third aspect of theinvention, the detector is moved with respect to the subject while thesensor is operating, and the control means causes, based on the signalfrom the sensor, the driving means to position, move and stop thedetector automatically.

Still another object of the invention is to provide a sensor which canreliably detect an object even if a light-reflecting object is locatedin its neighborhood.

In a fourth aspect of this invention, there is provided a sensor whichcomprises: at least one light-emitting element for emitting a lightbeam; at least one light-receiving element, opposing the light-emittingelement, spaced apart therefrom by a predetermined distance, and locatedin the same plane as the light-emitting element; and at least one slitunit located between the at least one light-emitting element and the atleast one light-receiving element. This sensor is characterized in thatthe slit unit is a honeycomb slit unit.

The at least one slit unit located between the at least onelight-emitting element and the at least one light-receiving elementprevents the beam emitted by the at least one light-emitting elementfrom being applied to a reflector, if located nearby, or the lightscattered or reflected from such a reflector from reaching the at leastone light-receiving element. If the slit unit is a honeycomb slit unit,then it effectively prevents undesired application of a beam to areflector and undesired application of scattered or reflected light tothe at least one light-receiving element.

In a fifth aspect of the present invention, there is provided a sensorwhich comprises: an array of light-emitting elements for emitting beams;an array of light-receiving elements opposing the light-emittingelements, spaced apart therefrom by a predetermined distance, andarranged in the same plane as the light-emitting elements, for receivingthe beams emitted from the light-emitting elements; and means forapplying the beam emitted from each light-emitting element sequentiallyto the light-receiving elements, repeatedly a number of times which isan integral multiple of the number of the light-emitting elements.

In a sixth aspect of the present invention, there is provided a sensorwhich comprises: two parallel arrays of light-emitting elements; atleast two light-receiving elements located at the ends of each of thearrays of light-emitting elements; and means for repeatedly applying thebeams sequentially emitted from the light-emitting elements of one ofthe array to each of at least two light-receiving elements located atthe ends of the other array.

The sensors according to the fifth and sixth aspects of this inventionare characterized in that it further comprises at least one honeycombslit unit extending between the two arrays of light-emitting elements.

In the sensor according to the fifth aspect of the invention, the beamemitted from each light-emitting element is sequentially applied to thelight-receiving elements, repeatedly a number of times which is anintegral multiple of the number of the light-emitting elements. In thesensor according to the sixth aspect of the invention, the beamssequentially emitted from the light-emitting elements of one of thearray are repeatedly applied to each of at least two light-receivingelements located at the ends of the other array. In either sensor, notonly parallel light beams but also slant, non-parallel light beams areused to detect any object existing between the array of light-emittingand -receiving elements. This helps increase the precision of detectingan object. Use of a honeycomb slit unit, extended between the two arraysof light-emitting and -receiving elements, serves to enhance further theprecision of detecting an object.

In a seventh aspect of the invention, there is provided a sensor whichhas a honeycomb slit unit comprising a compressed honeycomb structuremade of a thin plate and coated with dark mat paint, and a frame holdingthe compressed honeycomb structure.

Since the slit unit comprises a compressed honeycomb structure, thedepth, diameter and width of the individual slits can easily beadjusted. As a result, the angle at which a light beam is appliedthrough each slit can be reduced.

In an eighth aspect of this invention, there is provided a sensor whichcomprises: an array of first to Nth light-emitting elements; an array offirst to Nth light-receiving elements opposing the first to Nthlight-emitting elements, respectively, spaced apart therefrom by apredetermined distance, and located in the same plane as the first toNth light-emitting elements; means for repeating a sequence of the stepsof:

causing the first light-emitting element to emit beams and the first andsecond light-receiving elements to receive the beams and generatesignals;

causing the second light-emitting element to emit beams and the first,second and third light-receiving elements to receive the beams andgenerate signals;

causing any Mth light-emitting element (1<M<N) to emit beams and the(M-1)th, Mth and (M+1)th light-receiving elements to receive the beamsand generate signals; and

causing the Nth light-emitting element to emit beams and the (N-1)th andNth light-receiving elements to receive the beams and generate signals;and

means for recording the beams emitted by the first to Nth light-emittingelements and the signals generated by the first to Nth light-receivingelements, checking the beams and signals against the positions of thefirst to Nth light-emitting elements and the positions of the first toNth light-receiving elements, thereby detecting a position of a subjectexisting between the array of the first to Nth light-emitting elementsand the array of the first to Nth light-receiving elements.

In a ninth aspect of this invention, there is provided a sensor whichcomprises: an array of first to Nth light-emitting elements; an array offirst to Nth light-receiving elements opposing the first to Nthlight-emitting elements, respectively, spaced apart therefrom by apredetermined distance, and located in the same plane as the first toNth light-emitting elements; and means for performing two sequences ofsteps in each cycle of operation when no object exists between the arrayof first to Nth light-emitting elements and the array of first to Nthlight-receiving element.

The first sequence of steps consisting of the steps of:

causing the first light-emitting element to emit beams and the first andsecond light-receiving elements to receive the beams and generatesignals;

causing the second light-emitting element to emit beams and the first,second and third light-receiving elements to receive the beams andgenerate signals;

causing any Mth light-emitting element (1<M<N) to emit beams and the(M-1)th, Mth and (M+1)th light-receiving elements to receive the beamsand generate signals; and

causing the Nth light-emitting element to emit beams and the(N-1)th andNth light-receiving elements to receive the beams and generate signals.

The second sequence of steps consisting of the steps of:

causing the first light-emitting element not to emit beams and thesecond and second light-receiving elements to generate signals;

causing the second light-emitting element not to emit beams and thefirst, second and third light-receiving elements to generate signals;

causing any Mth light-emitting element (1<M<N) not to emit beams and the(M-1)th, Mth and (M+1)th light-receiving elements to generate signals;and

causing the Nth light-emitting element not to emit beams and the(N-1)thand Nth light-receiving elements to generate signals.

With the sensors of the eighth and ninth aspects of the presentinvention it is possible, by virtue of the above-described sequences ofsteps performed, to specify the position of any object existing betweenthe two arrays of light-emitting and -receiving elements and todetermine whether or not any one of the light-emitting and -receivingelements is out of order.

Any sensor, described above, according to the present invention, has atleast one slit unit in front of the array of light-emitting elements orthe array of light-receiving elements. Hence, the sensor can detect anyobject existing between the arrays, not influenced by light scattered orreflected from a reflector, if any, located near the sensor. Since theslit unit comprises a compressed honeycomb structure, the size of theindividual slits can easily be adjusted in accordance with the positionof the reflector and the those of the light-emitting and -receivingelements.

Additional objects and advantages of the present invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the present invention.The objects and advantages of the present invention may be realized andobtained by means of the instrumentalities and combinations particularlypointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe present invention and, together with the general description givenabove and the detailed description of the preferred embodiments givenbelow, serve to explain the principles of the present invention inwhich:

FIGS. 1A and 1B are diagrams showing two alternative orbits along whichthe detector of a conventional scintillation camera may be moved;

FIG. 2 is schematic representation of a conventional sensor;

FIGS. 3A and 3B are diagrams for explaining the disadvantages of theconventional sensor;

FIG. 4 is a perspective view showing a scintillation camera according toan embodiment of the present invention;

FIGS. 5A and 5B are diagrams showing the detector used in the camera ofFIG. 4 and the ultrasonic sensors attached to the detector;

FIG. 6 is a side view showing the detector and the reflection-typeoptical sensors attached to the detector;

FIG. 7 is a side view showing the detector and the air-mat sensorattached to the detector;

FIGS. 8A, 8B, and 8C are diagrams showing the detector and the tensionsensors connected to the detector;

FIGS. 9A, 9B, and 9C are diagrams showing the detector and thecounter-type optical sensors connected to the detector;

FIGS. 10A and 10B are diagrams showing the detector and the counter-typeoptical sensors attached to the detector;

FIG. 11 is a block diagram showing a scintillation camera according to afirst embodiment of the present invention;

FIG. 12 is a diagram illustrating the positional relationship between asubject and the detector incorporated in the scintillation camera;

FIGS. 13A and 13B are diagrams schematically illustrating the detectorsection of the scintillation camera;

FIG. 14 is a schematic representation of a subject, for explaining howto locate the body axis of the subject;

FIG. 15 is a flow chart for explaining the method of locating the bodyaxis;

FIG. 16 is a diagram schematically showing a subject, for explaining howSPECT data is acquired from the subject in stepwise mode by aconventional scintillation camera;

FIG. 17 is a flow chart for explaining how the conventionalscintillation camera is operated to acquire SPECT data from the subjectin the stepwise mode;

FIG. 18 is a diagram schematically showing a subject, for explaining howSPECT data is acquired from the subject in the stepwise mode by thescintillation camera according to a second embodiment of the invention;

FIG. 19 is a flow chart for explaining how a scintillation camera,according to the second embodiment of the invention, is operated inorder to acquire SPECT data from the subject in the stepwise mode;

FIG. 20 is a flow chart explaining, in detail, Step C7 which is one ofthe steps for operating the scintillation camera according to the secondembodiment of the invention;

FIG. 21 is a flow chart for explaining how the scintillation camera,according to the second embodiment of the invention, is operated inorder to acquire SPECT data from the subject in the continuous mode;

FIG. 22 is a flow chart for explaining how the detector of ascintillation camera, according to the invention, performs a scanningoperation while being moved in a horizontal direction, in order toacquire data from a subject;

FIG. 23 is a diagram for explaining a method of preventing an inchingmotion during the scanning operation;

FIG. 24 is a flow chart for explaining how the detector of thescintillation camera performs a scanning operation without making aninching motion;

FIG. 25 is a diagram for explaining the distance L, a conditionnecessary for starting the approach of the detector in the scanningoperation illustrated in FIG. 24;

FIGS. 26A And 26B are a front view and a side view, respectively, of ascintillation camera according to a fourth embodiment of the presentinvention;

FIG. 27 is a flow chart for explaining the operation of thescintillation camera shown in FIGS. 26A and 26B;

FIG. 28A is a diagram for explaining how the camera of FIGS. 26A and 26Boperates when a subject lies on the bed;

FIG. 28B is a diagram for explaining how the camera of FIGS. 26A and 26Boperates when no subject lies on the bed;

FIG. 29 is a diagram showing a first example of the sensor used in thepresent invention;

FIG. 30 is a perspective view of part of the honeycomb structure of oneof the identical slit units incorporated in the sensor shown in FIG. 16;

FIGS. 31A to 31E are diagrams for explaining a method of manufacturingthe slit unit;

FIG. 32 is a diagram for explaining the effect resulting from the use ofthe slit units manufactured by the method shown in FIGS. 31A to 31E;

FIGS. 33A and 33B are diagrams showing a second example of the sensor;

FIG. 34 is a diagram illustrating a third example of the sensor;

FIG. 35 is a diagram showing a fourth example of the sensor;

FIG. 36 is a diagram showing a fifth example of the sensor;

FIG. 37 is a diagram showing a sixth example of the sensor;

FIG. 38 is a diagram illustrating a scintillation camera having a sensorof the type shown in FIGS. 33A and 33B; and

FIG. 39 is a diagram showing a path along which the detector of ascintillation camera according to the invention is moved to performhelical scanning.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described, with referenceto the accompanying drawings. In describing each embodiment, thecomponents identical to those of any other embodiment will be designatedat the identical reference numerals and will not be repeatedly describedin detail.

FIG. 4 shows a scintillation camera which is an embodiment of thepresent invention. More precisely, the figure shows the major componentsof the camera, such as a detector and a mechanism supporting thedetector.

As shown in FIG. 4, two parallel stand rails 40 are laid on the floor. Astand 42 is mounted on the rails 40 and can move back and forth in thedirections specified by A. A subject (not shown) lying on the bed 50bremains positioned with his or her body axis parallel to the directionsA, while data is acquired from the subject. On one side of the stand 42,a rotating plate 44 is mounted, which can rotate in the directionsspecified by B. An arm 46 is secured at one end to the peripheral edgeportion of the rotating plate 44. A detector 48 is attached to the otherend of the arm 46. The detector 48 can rotate around the isocenter a, asthe plate 44 rotates. The arm 46 include a mechanism (not shown) formoving the detector 48 toward and away from the subject in thedirections indicated by C.

Sensors are attached to the detector 48, for detecting whether or notthe detection surface (γ-ray incidence surface) of the detector 48 hasapproached the subject, at the body surface of the subject. The sensorsmay be of one of the various types which will be described below.

FIGS. 5A and 5B are diagrams showing the detector 48 and the ultrasonicsensors attached to the detector 48. More specifically, FIG. 5A is aside view showing the detector 48 and the ultrasonic sensor attached tothe detector 48, and FIG. 5B is a bottom view showing the detector 48and the ultrasonic sensor.

As shown in FIGS. 5A and 5B, two arrays of ultrasonic sensors 61 areattached to the front and rear of the detector 48, respectively. Thearrays of sensors 61 extend parallel to each other, in the widthwisedirection D (hereinafter referred to as "direction D") of a subject 50.Each ultrasonic sensor 61 emits ultrasonic waves to the body surface ofthe subject 50 and receives the waves reflected therefrom, measures thedistance between it and the body surface from the time lapsing from theemission of waves to the receipt thereof, and produces a signal when thedistance thus measured changes to a predetermined value.

The output signal of each ultrasonic sensor 61 is in an ON state whenthe detecting surface of the detector 48 approaches the subject 50, at apredetermined distance from the body surface of the subject 50, and isin an OFF state when the detecting surface of the detector 48 is locatedat a distance longer than the predetermined distance from the bodysurface of the subject 50. This definition of the ON state and OFF stateof the output signal of each ultrasonic sensor 61 will be applied,unless otherwise specified, to all types of sensors used in theinvention and which will be described later. A housing 100 is providedfor housing the sensors 61 when not in use.

FIG. 6 is a side view showing the detector 48 and the reflection-typeoptical sensors attached to the detector 48. As shown in FIG. 6, twoarrays of reflection-type optical sensors 62 are attached to the frontand rear of the detector 48, respectively, and extend parallel to eachother, in the direction D, in the same way as the arrays of ultrasonicsensors 61 shown in FIGS. 5A and 5B. Each optical sensor 62 emits alight beam to the body surface of the subject 50 and receives the beamreflected therefrom, measures the distance between it and the bodysurface from the time lapsing from the emission of the light beam to thereceipt thereof, and generates a signal when the distance thus measuredchanges to a predetermined value. A housing 100 is provided for housingthe sensors 62 when not in use.

FIG. 7 is a side view showing the detector 48 and an air-mat sensor. Theair-mat sensor comprises an air mat 63 and an air-pressure sensor (notshown) contained in the air mat 63. The air mat 63 is attached to thedetection surface of the detector 48, covering the entire detectionsurface and filled with air at a predetermined pressure. The air mat 63has a uniform thickness, which is equal to the distance by which each ofthe ultrasonic sensors 61 (FIGS. 5A and 5B) or each of the opticalsensors 62 (FIG. 6) is spaced apart from the body surface of the subject50 when the sensor 61 or 62 produces a signal. When the air mat 63contacts the subject 50, the air pressure in the mat 63 changes. Theair-pressure sensor, contained in the air mat 63, detects this change inthe air pressure and produces a detection signal. A housing 100 isprovided for housing the sensor 63 when not in use.

FIGS. 8A, 8B, and 8C are diagrams showing the detector 48 and thetension sensors 64 connected to the detector 48. More specifically, FIG.8A is a side view showing the detector 48 and the tension sensors 64,FIG. 8B is a front view as seen from the head of a subject 50, and FIG.8C is a bottom view of the detector 48. A housing 100 is provided forhousing the sensors 64 when not in use.

A plurality of strings 56 are stretched beneath the detection surface ofthe detector 48, extending parallel to one another as shown in FIG. 8C.They are spaced away from the detection surface of the detector 48 by apredetermined distance. This distance is equal to the distance by whicheach of the ultrasonic sensors 61 (FIGS. 5A and 5B) or each of theoptical sensors 62 (FIG. 6) is spaced apart from the body surface of thesubject 50 when the sensor 61 or 62 produces a signal. Two tensionsensors 64 are connected to the ends of one string 65. When the string65 contacts a subject 50, its tension changes. The tension sensors 64detects the change in tension and generate a detection signal. Thestrings 65 may be replaced by a strip of cloth.

FIGS. 9A, 9B, and 9C are diagrams showing the detector 48 and thecounter-type optical sensors connected to the detector 48. Morespecifically, FIG. 9A is a side view showing the detector 48 and thecounter-type optical sensors, FIG. 9B is a front view as seen from thehead of a subject 50, and FIG. 9C is a bottom view of the detector 48.

As shown in FIGS. 9A and 9B, an array of light-emitting elements 11 isconnected to one side of the detector 48, and an array oflight-receiving elements 12 to the other side of the detector 48. Botharrays extend in the direction indicated by A. Each of the counter-typeoptical sensors comprises a light-emitting element 11 and alight-receiving element 12. As shown in FIG. 9C, the optical axis ofeach counter-type optical sensor extends in the direction D and parallelto the optical axis of any other counter-type optical sensor. As can beseen from FIG. 9B, the optical axes of the counter-type optical sensorsare spaced away from the detection surface of the detector 48 by apredetermined distance. This distance is equal to the distance by whicheach of the ultrasonic sensors 61 (FIGS. 5A and 5B) or each of theoptical sensors 62 (FIG. 6) is spaced apart from the body surface of thesubject 50 when the sensor 61 or 62 generates a signal. The outputsignal of each counter-type optical sensor is in an ON state when anobject interrupts the light beam traveling from the light-emittingelement 11 toward the light-receiving element 12, and is in an OFF statewhen no object interrupts the light beam. A housing 100 is provided forhousing the light-emitting elements 11 and the light-receiving elements12 when not in use.

FIGS. 10A and 10B are diagrams showing the detector 48 and thecounter-type optical sensors attached to the detector 48. Morespecifically, FIG. 10A is a side view showing the detector 48 and thecounter-type optical sensors, and FIG. 10B is a front view as seen fromthe head of a subject 50.

As shown in FIG. 10A, three arrays 14 of light-emitting elements 11stand on the floor, extending vertically and equidistantly spaced apartin the direction specified by A. Similarly, three arrays 15 oflight-emitting elements 12 stand on the floor, extending vertically andequidistantly spaced apart in the direction indicated by A. As shown inFIG. 10B, the arrays 14 are spaced from the arrays 15 respectively, inthe direction specified by D, by a distance longer than the width of thedetector 48 and the body width of a subject 50. Each of the counter-typeoptical sensors comprises a light-emitting element 11 of one array 14and the associated light-receiving element 12 of the array 15 opposingthe array 14. As shown in FIG. 10B, the optical axes 13 of thecounter-type optical sensors extend in the direction D and parallel toone another, and are spaced apart, from one another, equidistantly. Theoutput signal of each light-receiving element 12 decreases in magnitudewhen an object interrupts the light beam traveling from the associatedlight-emitting element 11 toward the light-receiving element 12. Hence,the number of the light-receiving elements 12, whose output signals haveyet to decrease in magnitude, indicates the distance between thedetection surface of the detector 48 and the body surface of the subject50, since the optical axes 13 of the counter-type optical sensors arespaced apart from one another equidistantly.

The sensor system shown in FIGS. 10A and 10B is in an ON state when thedetection surface of the detector 48 is spaced apart from the bodysurface of the subject 50 by a predetermined distance, and is in an OFFstate when the detection surface of the detector 48 is spaced apart fromthe body surface of the subject 50 by a distance longer than thepredetermined one. The predetermined distance is equal to the distanceby which each of the ultrasonic sensors 61 (FIGS. 5A and 5B) or each ofthe optical sensors 62 (FIG. 6) is spaced apart from the body surface ofthe subject 50, when the sensor 61 or 62 produces a signal. Neither thearrays 14 of light-emitting elements nor the arrays 15 oflight-receiving elements need to stand on the floor. Instead, they maybe secured to the sides of the detector 48 so as to move as the detector48 is moved in the directions specified by A. Furthermore, the threearrays 14 may be replaced by three light-emitting elements 11, and thethree arrays 15 by three light-receiving elements 12 opposing the threelight-emitting elements 11, respectively, provided that each pair of theassociated elements 11 and 12 move in the directions indicated by C toscan the subject 50, along his or her side.

In the present embodiment, sensors of any one of the types describedabove with reference to FIGS. 5A to 10B can be employed. Sensors of anytype described above can also be used in other embodiments of theinvention, which will be described below.

FIG. 11 is a block diagram illustrating a scintillation camera accordingto a first embodiment of the present invention. FIG. 12 shows thepositional relationship between a subject 50 and the detector 48incorporated in the scintillation camera.

As shown in FIG. 11, the scintillation camera comprises a sensor 10, asensor control circuit 20, a frame control circuit 30, a detectorrotating unit 32, a stand driving unit 34, a detector moving unit 36 andan image processing unit 38. The sensor 10 is of any one of the typesdescribed above. The sensor control circuit 20 is designed to detectwhether the sensor 10 is in an ON state or an OFF and to turn on and offeach of the light-emitting elements and each of the light-receivingelements, all incorporated in the sensor 10. The frame control circuit30 is used to control the motion of the frame (not shown) of thescintillation camera. The detector rotating unit 32 is provided forrotating the detector 48 mounted on the frame. The stand driving unit 34is designed to move the stand of the scintillation camera horizontally.The detector moving unit 36 is provided for moving the detector 48toward and away from a subject 50a (FIG. 12) or a bed 50b (FIG. 12) onwhich the subject 50a is lying, so that the detector 48 may remain at apredetermined distance from the subject 50a or from the bed 50b. Theimage processing unit 38 is designed to process the image data acquiredby the detector 48.

The operation of the scintillation camera shown in FIG. 11 will bedescribed, based on the assumption that the sensor 10 is a counter-typeoptical sensor of the type shown in FIGS. 9A to 9C though it may be ofany other type described above.

The sensor control circuit 20 drives the first to Nth sensor units ofthe sensor 10, each consisting of a light-emitting element and alight-receiving element--at high speed one after another. The circuit 20detects whether each sensor unit is on or off, and supplies the framecontrol circuit 30 with data which represents that each sensor unit isin an ON state or an OFF state. Since their ON/OFF states are detectedat high speed, the first to Nth sensor units jointly operate as if theywere a single sensor, which is the sensor 10.

The frame control circuit 30 controls the detector rotating unit 32, thestand driving unit 34 and the detector moving unit 36 in accordance withthe data supplied from the sensor control circuit 20 and predetermineddata-acquisition conditions, to thereby move the detector 48 in adesired manner with respect to the subject 50a and the bed 50b. Underthe control of the circuit 30, the detector rotating unit 32 rotates thedetector 48 around the subject 50a and the bed 50b in the directionsspecified by A, the stand driving unit 34 moves the stand 42 (FIG. 4),thereby moving the detector 48 in the direction D, and the detectormoving unit 36 moves the detector 48 away from the subject 50a and thebed 50b in the direction of arrow B or toward the subject 50a and thebed 50b in the direction of arrow C. Thus rotated and linearly driven,the detector 48 moves around the subject 50a and 50b in a desired orbit.In the description that follows, the motion of the detector 48 in thedirections indicated by A will be referred to as "rotation," that of thedetector 48 in the direction of arrow B as "far," and that of thedetector 48 in the direction of arrow C as "near."

In the scintillation camera, as already indicated, the frame controlcircuit 30 controls the detector moving unit 36 in accordance with theON/OFF state of the sensor 10. Hence, the detector 48 make a far or anear motion thereby so as to be located at a predetermined distance awayfrom the body surface of the subject 50a or from the bed 50b.

Every time the detector 48 is rotated at a predetermined angle, forexample, 90°, it acquires the data representing the positions of thesubject 50a and the bed 50b. The position data is supplied to the imageprocessing unit 38. The unit 38 extracts data, representing the ridgeline of the subject 50a, from the position data which the detector 48acquires as it rotates once around the subject 50a and the bed 50b. Theridge-line data, which shows the ridge line with precision, can be usedas absorption-correcting data.

How the detector 48 is moved to a prescribed position to acquire datafrom the subject 50a will be described in detail, with reference toFIGS. 13A and 13B. The components identical to those shown in FIG. 12are denoted by the same numerals in FIGS. 13A and 13B and will not bedescribed in detail. Like FIG. 12, FIG. 13A is a front view as seen fromthe head of a subject 50a. FIG. 13B is a side view.

As the detector 48 is moved in the directions indicated by arrows A, B,C, and D shown in FIGS. 13A and 13B, the sensor control circuit 20 keepsmonitoring the ON/OFF state of the sensor 10. The circuit 20 suppliesthe frame control circuit 30 with the data showing that the sensor 10 isin the ON state or the OFF state. The circuit 30 controls the detectormoving unit 36 in accordance with the data so that the detector 48 maybe located at a predetermined distance from the body surface of thesubject 50a or from the bed 50b. Arrows D in FIG. 13B indicate theopposite directions in which the detector 48 is moved along the bodyaxis of the subject 50a, from head to toe and other way around.

The detector 48 may contact the subject 50a or the bed 50b on the bed50b while being rotated in either of the directions of arrow A, whilebeing moved in either of the horizontal directions of arrow D, or whileapproaching the subject 50a in the direction of arrow C. Nonetheless, itis unnecessary for an operator of the scintillation camera to take painsto prevent the detector 48, from contacting the subject 50a or the bed50b. This is because the sensor 10 attached to the detector 48 serves tolocate, as described above, the detector 48 always at the predetermineddistance from the body surface of the subject 50a or from the bed 50b.

More specifically, when the sensor 10 detects the subject 50a or the bed50b while the detector 48 is being rotated in either direction of arrowA, the detector 48 automatically makes a far motion. When the sensor 10detects the subject 50a or the bed 50b while the detector 48 is beingmoved parallel to the subject 50a or the bed 50b in either direction ofarrow D, the detector 48 automatically makes a far motion. When thesensor 10 detects the subject 50a or the bed 50b while the detector 48is approaching the subject 50a or the bed 50b in the direction of arrowC, the detector 48 is automatically stopped.

Since the detector 48 stops approaching the subject 50a or the bed 50bor retreats therefrom in accordance with the ON/OFF state of the sensor10 which is detected while the detector 48 is rotating and horizontallymoving, the operator can move the detector 48 to a desired positionwithin a short time, without taking pains not to let the detector 48contact the subject 50a or the bed 50b.

It will now be explained how to locate the body axis of the subject 50awith the scintillation camera, with reference to FIGS. 14 and 15. FIG.14 is a schematic representation of the subject 50a, as viewed from thehead. FIG. 15 is a flow chart for explaining the method of locating thebody axis. In FIG. 14, the center of rotation of the detector 48 isdesignated as point O, and the body axis located by computation isdenoted as point O'.

As the detector 48 rotates around the subject 50a, clockwise in FIG. 14,it assumes a 0°-position at the back of the subject, a 90°-position onthe left side of the subject, a 180°-position in front of the subject, a270°-position on the right side of the subject, a 360°-position(identical to the 0°-position) at the back of the subject.

Referring to FIG. 15, the detector 48 is rotated to the 0°-position inStep A1. Next, in Step A2, the detector 48 is made to approach the bed50b until the sensor 10 detects the ON state. In Step A3, the detector48 is stopped when the sensor 10 detects the ON state, and the datarepresenting the position of the detector 48, i.e., x-axis coordinatevalue and y-axis coordinate value, is stored into a memory. Then, inStep A4, the detector 48 is rotated clockwise through 90°. In Step A5,it is determined whether or not the detector 47 has been rotated through360° around the subject 50a, and back to the 0°-position. If Not in stepA5, the flow returns to Step A2. If it has, the flow goes to Step A6, inwhich the following values dx and dy are calculated:

    dx=(d270°-d90°)/2

    dy=(d180°-d0)/2

where d0°, d90°, d180° and d270° are the XY-coordinate positions thecenter of the detector 48 takes, as the detector 48 move to the0°-position, the 90°-position, the 180°-position and the 270°-position,respectively.

Thanks to the use of the sensor control circuit 20 and the like, whichserve to keep the detector 48 spaced apart from the subject 50a, it ispossible to automatically acquire data items dx and dy, which correctlydefine the position of the body axis O' of the subject 50a.

A device (not shown) designed to adjust the position of the subject 50ais operated until the distance between the center O of rotation of thedetector 48 and the body axis O' thus located is reduced to nil. As aresult of this, the subject 50a is automatically placed in a desirableposition with respect to the detector 48--that is, he or she ispositioned with the body axis passing through the center O of rotationof the detector 48. Since the subject 50a has been detected thedesirable position, the detector 48 can then proceed to acquire accuratedata from the subject 50a. The data are so accurate that a tomographicimage of the subject, reconstructed from the data, will have highquality. Furthermore, once the subject 50a has been placed at thedesirable position, it is no longer necessary for the operator to makefar or near motion of the detector 48 to the subject 50a. Thus, thescintillation camera can acquire data from the subject 50a with highefficiency.

A scintillation camera according to a second embodiment, which isdesigned for use in a single photon emission computed tomographyapparatus (hereinafter referred to as "SPECT apparatus"), will bedescribed in the following.

This scintillation camera is similar in structure to the scintillationcamera shown in FIG. 11, and its structure, therefore, will not bedescribed in detail. The camera can acquire SPECT data from a subject intwo modes, i.e., stepwise data-acquisition mode and continuousdata-acquisition mode. In the stepwise data-acquisition mode, thedetector acquires SPECT data every time it is stopped after it has beenrotated through a prescribed angle of, for example, 60°. In thecontinuous data-acquisition mode, the detector continuously acquiresdata while rotating around the subject without pause.

The stepwise acquisition of SPECT data will be described in greaterdetail, with reference to FIGS. 16 to 20.

How the conventional scintillation camera acquires SPECT data in thestepwise mode will be first described, with reference to FIGS. 16 and17. FIG. 16 is a diagram schematically showing a subject, for explaininghow SPECT data is acquired from the subject in stepwise mode by aconventional scintillation camera. FIG. 17 is a flow chart forexplaining how the conventional scintillation camera is operated toacquire SPECT data from the subject in the stepwise mode.

Referring to the flow chart of FIG. 17, the afore-mentioned 4-pointdetermination method is performed in Step B1 in preparation for theacquisition of SPECT data. That is, as is shown in FIG. 16, the dataitems representative of four data-acquisition positions A1 to A4,angularly spaced apart by 90°, are input before the detector of thecamera is moved around a subject 50a to scan the subject. Next, in StepB2, an elliptical orbit L, in which the detector 48 is to move stepwise,to acquire SPECT data from the subject 50a, is calculated. Then, in StepB3, the detector 48 staying at the data-acquisition position A3, forexample, starts acquiring SPECT data from the subject 50a. In Step B4,the detector 48 is rotated toward the next data-acquisition position A4in the orbit L, and is simultaneously moved toward or away from thesubject 50a. In Step B5, the contact sensor secured to the detector 48determines whether or not the detection surface 48a of the detector hastouched the body surface of the subject 50a or the bed 50b during thetransit from the position A3 to the position A4. If Yes, the flow goesto Step B6, in which the detector 48 is moved away from the subject 50a.More precisely, as shown in FIG. 16, the detector 48 is stopped fromrotating around the subject 50a at point F1 lying on the orbit L andlocated between the positions A3 and A4. Then, it makes a far motion topoint F2. Next, in Step B7, a new elliptical orbit M is calculated,which passes both points F2 and A4. In Step B8, the detector 48 isrotated around the subject 50a from point F2 to the position A4 alongthe new elliptical orbit M.

If No in Step B5, that is, if the detector 48 has not touched the bodysurface of the subject 50a or the bed 50b during the transit from thedata-acquisition position A3 to position A4, then the flow jumps to StepB9. In Step B9, it is determined whether or not the detector 48 hasreached the last data-acquisition position. If No, the flow returns toStep B3. If Yes, the acquisition of the SPECT data is terminated.

With the scintillation camera according to the second embodiment of thisinvention, no steps whatsoever, equivalent to Steps B1 and B2, need beperformed as will be explained in the following, with reference to FIGS.18, 19 and 20. FIG. 18 is a diagram schematically showing a subject, forexplaining how SPECT data is acquired from the subject in the stepwisemode by the scintillation camera. FIG. 19 is a flow chart for explaininghow the camera is operated to acquire SPECT data from the subject in thestepwise mode. FIG. 20 is a flow chart explaining, in detail, Step C7which is one of the steps for operating the camera.

With reference to FIGS. 18 and 19 it will be explained how thescintillation camera acquires SPECT data from the subject in thestepwise mode.

As has been indicated, the data acquisition is started withoutperforming the 4-point determination method. First, in Step C1, thesensor control circuit 20 determines whether the sensor 10 detects an ONstate or an OFF state, as illustrated in FIG. 18. If the sensor 10 is inthe OFF state, the flow goes to Step C2, in which the detector 48 makesnear motion to the subject 50a. In Step C3, it is determined whether thesensor 10 has detected the ON state or the OFF state. If the sensor 10is in the OFF state, the flow returns to Step C3. If the sensor 10 is inthe ON state, the flow goes to Step C4, in which the detector 48 isstopped from rotating around the subject 50a. Then, the flow goes toStep C5.

In Step C5, the data representing the position at which the detector 48is stopped is stored into a storage device (not shown). Not only thedata, but also any other data showing the position the detector 48 willdetect every time it is rotated around the subject 39a through apredetermined angle is stored into the storage device. These data itemsdefine the ridge line of the subject and can be used asabsorption-correcting data. Hence, the ridge line of the subject isautomatically obtained.

Then, in Step C6, the detector acquires SPECT data from the subject fora predetermined period of time. In Step C7, the detector 48 isautomatically rotated around the subject and moved with respect theretoin accordance with the ON/OFF state of the sensor 10, as will bedescribed later in detail. In Step C8, it is determined whether or notthe detector 48 has reached the position where it should stop acquiringSPECT data. If Yes, the detector 48 stops acquiring the SPECT data. IfNo, the flow returns to Step C5.

With reference to FIG. 20, Step C7 will be explained in more detail, inwhich the detector is automatically rotated around the subject and movedwith respect thereto, in accordance with the ON/OFF state of the sensor10.

First, in Step D1 the detector 48 is rotated around the subject towardthe next data-acquisition position. In Step D2, it is determined whetherthe sensor 10 is in the ON state or the OFF state while the detector 48is being rotated. If the sensor 10 is in the ON state, the flow goes toStep D6. If the sensor 10 is in the OFF state, the flow goes to Step D3.The detector 48 keeps rotating, unlike the conventional scintillationcamera.

If it is detected in Step D2 that the sensor 10 is in the OFF state, thesensor control circuit 20 detects that the detector is spaced away fromthe subject. Hence, Step D3 is performed, in which the detector 48starts near motion to the subject. In Step D4, it is determined whetherthe sensor 10 has detected the ON state or the OFF state. If the sensor10 is in the ON state, the flow goes to Step D5, in which the detectoris made to stop near motion to the subject.

If it is detected in Step D2 that the sensor 10 is in the OFF state,indicating the possibility that the detector 48 may contact the subject50a, the flow goes to Step D6. In Step D6, the detector 48 starts farmotion from the subject 50a. In Step D7, it is determined whether thesensor 10 has detected the ON state or the OFF state. If the sensor 10is in the ON state, the flow goes to Step D8, in which the detector isstopped from far motion from the subject. If the sensor 10 is in OFFstate, the flow returns to Step D7. Thus, the detector makes far motionfrom the subject until it reaches a position at a predetermined distancefrom the subject.

Then, in Step D9, it is determined whether or not is the detector 48 hasreached the next data-acquisition position. If No, the flow returns toStep D2. If Yes, the detector 48 is stopped from rotating, and the flowgoes to Step D10. In Step D10, it is determined whether the sensor 10has detected the ON state or the OFF state. If the sensor 10 is in theON state, that is, if the detector is located very close to the subject50a or the bed 50b, Step C7 is terminated. If the sensor 10 is in theOFF state, that is, if the detector is at a long distance from thesubject 50a or the bed 50b, the flow goes to Step D11, in which thedetector 48 is made to near motion to the subject 50a or the bed 50b. InStep D12, it is determined whether the sensor 10 has detected the ONstate or the OFF state. If the sensor 10 is in the OFF state, Step D12is repeated until the sensor 10 detects the ON state. When the sensor 10detects the ON state, the flow goes to Step D13, in which the detector48 is stopped from near motion the subject 50a or the bed 50b.

Until the detector 48 reaches the last data-acquisition position, it isrotated around the subject 50a in the orbit L as illustrated in FIG. 18.When the detector 48 reaches the last data-acquisition position, theSPECT data of the subject 50a and the bed 50b and the ridge line datathereof have already been obtained.

After the near motion of the detector 48 to the subject 50a and the farmotion thereof from the subject 50a (for example, after Step D5, Step D8and Step D13), a delay may be provided so that the detector 48 need notmake any unnecessary minute motion, such as inching motion. Moreover,the detector 48 can be rotated in an accurate orbit around the subject50a, since it is automatically moved toward and away from the subject50a at an appropriate speed. Thus, the detector is prevented fromcontacting the subject 50a or the bed 50b.

According to the present invention, the sensor 10 may obtain area datawhile the detector 48 is retreating from the subject 50a, and the areadata may be stored into a memory (not shown). If the amount of area dataincreases, the speed at which the detector is retreating is increased,to thereby prevent the detector 48 from contacting the subject 50a orthe bed 50b. In this case, the detector can be continuously moved evenif the subject moves, to an optimal position with respect to the subjectwho has just moved.

With reference to FIG. 21, it will be described how the scintillationcamera of the invention acquires SPECT data from a subject in thecontinuous data-acquisition mode.

First, in Step E1 the detector 48 starts to rotate around the subject50a and simultaneously begins acquiring SPECT data from the subject 50a.In Step E2, it is determined whether the sensor 10 has detected the ONstate or the OFF state. If the sensor 10 is in the ON state, the flowgoes to Step E6. If the sensor 10 is in the OFF state, the flow goes toStep E4. In Step E3 or Step E6, the detector 48 is not stopped fromrotating, unlike the conventional data-acquisition method illustrated inFIG. 17.

If it is determined in Step E2 that the sensor 10 is in the OFF state,the sensor control circuit 20 detects that the detector 48 is spacedaway from the subject. Hence, Step E3 is performed, in which thedetector 48 is started on a near motion toward the subject. In Step E4,it is determined whether the sensor 10 has detected the ON state or theOFF state. If the sensor 10 is in the OFF state, Step E4 is repeateduntil the sensor 10 detects the ON state. When the sensor 10 detects theON state, the flow goes to Step E5, in which the detector 48 is stoppedfrom near motion to the subject 50a.

If it is determined in Step E2 that the sensor 10 is in the OFF state,there is the possibility that the detector could be about to contact thesubject 50a or the bed 50b. Thus, in Step E6 the detector 48 is startedon a far motion from the subject 50a. In Step E7 it is determinedwhether the detector 48 has detected the ON state or the OFF state. Ifthe sensor 10 is in the ON state, Step E7 is repeated until the sensor10 detects the OFF state. When the sensor 10 detects the OFF state, theflow goes to Step E8, in which the detector 48 is stopped from farmotion from the subject 50a.

The flow goes from Step E5 or E6 to Step E9, in which it is determinedwhether or not the detector 48 has reached the last data-acquisitionposition. If No, the flow returns to Step E2. If Yes, the flow goes toStep E10, in which the detector 48 is stopped from rotating around thesubject 50a.

During the continuous rotation of the detector 48, a data itemrepresenting the position of the detector 48 is obtained every time itis rotated around the subject 39a, through a prescribed angle. The dataitems thus obtained, while the detector 48 is rotating are stored into astorage device. These data items define the ridge line of the subjectand can be used as absorption-correcting data. Hence, the ridge line ofthe subject is automatically obtained.

Also in the continuous data-acquisition mode, a delay may be providedafter the near motion of the detector 48 to the subject 50a and the farmotion thereof from the subject 50a (for example, after Step E5 and StepE8), so that the detector 48 need not make an unnecessary minute motion,such as inching motion. Moreover, the detector 48 can be rotated alongan accurate orbit around the subject 50a since it is automatically movedtoward and away from the subject 50a at an appropriate speed. Thus, thedetector is prevented from contacting the subject 50a or the bed 50b.

In the continuous data-acquisition mode, as well, the sensor 10 mayobtain area data while the detector 48 makes far motion from the subject50a, and the area data may be stored into a memory (not shown). If thearea data increases in amount, the speed at which the detector isretreating is increased, to thereby prevent the detector 48 fromcontacting the subject 50a or the bed 50b. In this case, the detectorcan be continuously moved even if the subject moves, to an optimalposition with respect to the subject who has just moved.

In the embodiments described above, the detector 48 acquires SPECT datafrom the subject 50a while it is being rotated around the subject 50a,either intermittently or continuously. According to the presentinvention, a detector may be moved horizontally along the body axis of asubject, as will be described with reference to the flow chart of FIG.22.

First, the data showing a scanning termination position is input byoperating a console (not shown). In Step F1, the stand driving unit 34starts moving the stand 42 in a horizontal direction, thereby moving thedetector 48 in the same direction. While being so moved, the detector 48keeps scanning a subject 50a and detecting the gamma-rays emitted fromthe radioisotope administered to the subject 50a.

In Step F2, the sensor control circuit 20 determines whether the sensor10 has detected an ON state or an OFF state while the detector 48 isbeing moved horizontally. If the sensor 10 is in the OFF state, that is,if the detector 48 is at a predetermined distance from the subject 50a,the flow goes to Step F3, in which the detector moving unit 36 (FIG. 11)moves the detector 48 toward the subject 50a. In Step F4, it isdetermined whether the sensor 10 has detected the ON state or the OFFstate. If the sensor 10 is in the OFF state, Steps F3 and F4 arerepeated until the sensor 10 detects the ON state. When the detector 48is moved to a predetermined distance from the subject 50a, the sensor 10detects the ON state. Then, the flow goes to Step F5, in which thedetector 48 is stopped from near motion to the subject 50a.

Next, in Step F6 the detector moving unit 36 starts moving the detector48 away from the subject 50a. In Step F7, it is determined whether thesensor 10 has detected the ON state or the OFF state. If the sensor 10is in the ON state, Step F6 and F7 are repeated until the sensor 10detects the OFF state. In Step F8, the detector 48 is moved further awayfrom the subject 50a for a predetermined time after the sensor 10 hasdetected the OFF state. In Step F9, upon elapse of the predeterminedtime, the detector 48 is stopped from far motion from the subject 50a.Then, the flow returns to Step F3, in which the detector 48 is startedon a near motion to the subject 50a.

Steps F6 to F9 will be explained in greater detail, with reference tothe flow chart of FIG. 23.

In FIG. 23, the solid line indicates a part of the ridge line of thesubject 50a, and the broken line represents the path along which thedetector 48 is moved. Further, in FIG. 23, point d1 indicates theposition the detector 48 takes as it starts faring in Step F6, point d2the position the detector 48 takes when the sensor 10 detects the OFFstate, and point d3 the position the detector 48 takes upon lapse of thepredetermined time after the sensor 10 has detected the OFF state. As isevident from the broken line, the detector 48 does not start near motionto the subject 50a the moment the sensor 10 detects the OFF state.Rather, the detector 48 continues to far motion from the subject 50auntil the predetermined time has expired. Thus, the detector 48 does notrepeat a short near motion and a short far motion, making an unnecessaryzig-zag motion, generally known as "inching motion."

When the detector 48 reaches the scanning termination positionrepresented by the data input from the console, it is stopped fromscanning the subject 50a.

As described above, the detector 48 continues to far motion from thesubject 50a up to the expiration of the predetermined time, and thusmakes no inching motion whatever. Another, more efficient method ofpreventing an inching motion, which can be used if the sensor 10 is ofthe type shown in FIGS. 8A to 8C or the type shown in FIGS. 9A to 9C,will be described with reference to the flow chart of FIG. 24. In thefollowing description, it will be assumed that the sensor 10 comprisesthe counter-type optical sensors illustrated in FIGS. 9A to 9C.

This method is similar to the method illustrated in FIG. 22. It ischaracterized in that the flow does not immediately go to Step F3 whenat least one of the light-receiving elements 12 changes from the ONstate to the OFF state in Step F7. In other words, the detector 48 doesnot approach the subject 50a until a specific condition holds in StepF10. In Step F10 it is determined whether a predetermined time haselapsed from the time any one of the light-receiving elements 12 changesfrom the ON state to the OFF state or whether the detector 48 has moveda distance L from the point at which where the element 12 changes fromthe ON state to the OFF state.

With reference to FIG. 25, the distance L will be described. In FIG. 25,arrows A' indicates the direction in which the detector 48 is movedhorizontally. Assume that the detector 48 is moved along the subject50a, from head to toe, in order to acquire data from the subject 50a.When the detection surface of the detector 48 approaches a predetermineddistance from the subject 50a, or some of the light-receiving elements12 change from the OFF state to the ON state. The distance between theforemost one of the elements 12 which undergo this state change and therearmost light-receiving element 12_(N) is the distance L. The distanceL can be obtained at the time of designing the sensor 10 once theintervals at which the elements 12 are located are set. The distance Lis stored in a memory (not shown) incorporated in the frame controlcircuit 30 and is read therefrom whenever necessary and used in StepF10.

Since the detector 48 does not approach the subject 50a after thedetector 48 has detects the OFF state (Step f7) until the predeterminedtime has elapsed or the detector 48 has moved the distance L, thedetector 48 is prevented from making an inching motion. That is, thedetector 48 continues to move horizontally until the predetermined timehas elapsed or the detector 48 has moved the distance L, while notapproaching the subject 50a. When it is determined in Step F11 that thesensor 10 has changed from the OFF state to the ON state, the flowreturns to Step F6, in which the detector 48 is started on a far motionfrom the subject 50a.

In the three embodiments described above, the detector remains at apredetermined distance away from the subject 50a throughout the dataacquisition. A fourth embodiment of the invention will be described, inwhich the sensor detects the presence or absence of a subject 50a on thebed 50b, the detectors automatically start and end the scanning atproper times, and the whole-body scanning length is calculated.

FIGS. 26A and 26B are a front view and a side view, respectively, of thescintillation camera according to the fourth embodiment of the presentinvention. The components of this camera, which are similar or identicalto those shown in FIGS. 11 and 12 are designated by the same numerals inFIGS. 26A and 26B and will not be described in detail.

The scintillation camera shown in FIGS. 26A and 26B differs in tworespects from the first to third embodiments. First, two detectors 48aand 48b are so located that their respective collimators 49a and 49boppose, with a bed 50a interposed between them. Second, the detectors48a and 48b are moved together in substantially the same manner by meansof a drive mechanism 35.

The scintillation camera has two optical sensors for detecting whether asubject lies on the bed 50b or not. The first optical sensor comprises alight-emitting elements 11a and a light receiving element 12b, and thesecond optical sensor comprises a light-emitting element 11b and alight-receiving element 12a. The elements 11a and 12a are held by asensor holder 26 attached to the detector 48a. Similarly, the elements11b and 12b are held by a sensor holder 26 secured to the detector 48b.

The elements 11a and 12b of the first sensor are positioned such thatthe element 12b can receive the light from the element 11a when nosubject lies on the bed 50b, and cannot receive the light when a subject50a lies on the bed 50b. Also, elements 11b and 12a of the second sensorare positioned such that the element 12a can receive the light from theelement 11b when no subject lies on the bed 50b and cannot receive thelight when a subject 50a lies on the bed 50b. The light-emittingelements 11a and 11b emit light beams which diverge at angles θ1 and θ2,respectively, so that both sensors may detect the absence or presence ofa subject on the bed 50b with high reliability, regardless of the bodythickness of the subject.

As shown in FIG. 26, the scintillation camera further comprises acontrol circuit 31 for controlling the drive mechanism 35 in accordancewith the detection signals supplied from the light-receiving elements12a and 12b.

The operation of the fourth embodiment of the invention will now bedescribed, with reference to FIG. 27 and FIGS. 28A and 28B. FIG. 27 is aflow chart explaining the operation of the embodiment. FIG. 28A explainshow the camera of FIGS. 26A and 26B operates when a subject 50a lies onthe bed 50b. FIG. 28B explains how the camera of FIGS. 26A and 26Boperates when no subject lies on the bed 50b.

First, as shown in FIG. 27, a subject 50a lies on the bed 50b in StepG1. Next, in Step G2, the detectors 48a and 48b are moved away from eachother, and the whole rotation angle is automatically set to 0°/180°,whereby both detectors are rotated to their initial positions from thepositions they take upon completion of the previous scanning. In StepG3, the detectors 48a and 48b are moved horizontally in the direction ofthe arrow shown in FIG. 26B, while operating the light-emitting elements11a and 11b and the light-receiving elements 12a and 12b.

When the detectors 48a and 48b are at the positions shown in FIG. 26B,the light beams emitted from the elements 11a and 11b reach thelight-receiving elements 12b and 12a, respectively. The light-receivingelement 12a generates a signal which indicates that no part of a subject50a exists between the elements 11b and 12a, and the light-receivingelement 12b generates a signal which indicates that no part of thesubject 50a exists between the elements 11a and 12b. These signals aresupplied to the control circuit 31. The magnitudes of the signalsdecrease when the sensors moved to the vertex of the subject 30a, andthe vertex interrupts the light beam emitted the light-emitting elements11a and 11b.

In Step G4, the control circuit 31 determines whether or not the sensorshave detected the vertex of a subject 50a, more precisely whether or notthe magnitudes of the signals from the light-receiving elements 12a and12b have decreased. If No, Steps G3 and G4 are repeated, whereby thecircuit 31 controls the drive mechanism 35 such that the mechanism 35continues to move the detectors 48 and 48b horizontally in the directionor the arrow (FIG. 26B). If Yes, in Step G4, that is, if the sensorshave been moved to the vertex of the subject 30a, the flow goes to StepG5.

In Step S5, the control circuit 31 causes the drive mechanism 35 to movethe detectors 48a and 48b further until the right edge of the effectiveview field (FIG. 26B) common to both detectors reaches the vertex of thesubject 50a. More specifically, data representing the distance betweenthe right edge of the effective view field and the elements 11a, 11b,12a and 12b, as measured in the horizontal direction, is stored in amemory connected to the control circuit 31, and the circuit 31 controlsthe drive mechanism 35 in accordance with this data, whereby themechanism 35 moves the detectors 48a and 48b for said distance.

Then, in Step G6, the detectors 48a and 48b perform so-called "windowopening," starting to acquire data from the subject 50a.

In Step G7, the control circuit 31 controls the drive mechanism 35 suchthat the detectors 48a and 48b are moved horizontally in predeterminedpaths, while maintaining the elements 11a, 11b, 12a and 12b in operativecondition. As a result of this, both detectors 48a and 48b continue toacquire data from the subject 50a. It is desirable that the paths of thedetectors 48a and 48b be as close to the subject 50a as possible so thatthe detectors 48a and 48b may acquire reliable data.

Thereafter, in Step 8, the control circuit 31 determines whether or notthe sensors (i.e., the elements 11a, 11b, 12a and 12b) have detected thetoes of the subject 30a, from the signals supplied from the sensors.

If No in Step 8, that is, if the sensors have not moved beyond the toesof the subject 50a and the magnitudes of the signals from thelight-receiving elements 12a and 12b therefore have not increased yet,Steps G7 and G8 are repeated, whereby the circuit 31 controls the drivemechanism 35 such that the mechanism 35 continues to move the detectors48 and 48b in the direction or the arrow (FIG. 26B) until the sensorsare moved beyond the toes of the subject 30a. If Yes in Step G8, thatis, if the sensors have been moved a little beyond the foot-tips of thesubject 30a, the flow goes to Step G9.

In Step S9, the control circuit 31 causes the drive mechanism 35 to movethe detectors 48a and 48b further until the right edge of the effectiveview field (FIG. 26B) reaches the toes of the subject 50a. Morespecifically, data representing the distance between the left edge ofthe effective view field and the elements 11a, 11b, 12a and 12b, asmeasured in the horizontal direction, is stored in a memory connected tothe control circuit 31, and the circuit 31 controls the mechanism 35 inaccordance with this data, whereby the mechanism 35 moves the detectors48a and 48b for said distance.

Next, in Step G10, the detectors 48a and 48b perform so-called "windowclosing," thus terminating the data acquisition from the subject 50a.

Finally, in Step G11, the control circuit 31 calculates the height ofthe subject 50a from the period between the time of detecting the vertexand the time of detecting the toes, and outputs the height, thuscalculated, as the whole-body scanning length. The whole-body scanninglength is displayed on a monitor (not shown).

As described above, both detectors 48a and 48b can be automaticallylocated at a scanning start position in the fourth embodiment, inpreparation for the acquisition of whole-body data from a subject 50a.Hence, it is easy for an operator to operate the scintillation cameraaccording to the fourth embodiment of the present invention.

In addition, the scanning termination position is automaticallydetected, and the detectors 48a and 48b are automatically stopped at thescanning termination position. Hence, it is unnecessary for the operatorto measure the height of the subject 50a and input the height as thewhole-body scanning length. Automatically measured, the whole-bodyscanning length is, in most cases, more accurate than the length theoperator may measure. This would help to achieve optimal display of thewhole body of the subject 50a.

Optical sensors, which may be used as in the sensor or sensors, used incombination with the first to fourth embodiments described above, willnow be described.

FIG. 29 shows a first example of the optical sensor 10 used in thepresent invention. As shown in FIG. 29, the sensor compriseslight-emitting elements 11 and light-receiving elements 11. The elements11 are arranged on the substrate 22 of a light-emission control circuitsubstrate 22, and the elements 12 on the substrate 24 of alight-reception control circuit. The elements 11 and the elements 12 arelocated in the same plane. Each light-receiving element 12 opposes theassociated light-emitting element 11 and can, therefore, detect anyobject located between it and the associated light-emitting element 11.

A pair of slit units arranged between the array of light-emittingelements 11 and that of light-receiving elements 12, extending alongthese arrays, respectively. They are provided to prevent the lightemitted from each element 11 from scattering and to prevent the lightreflected from any object between the arrays of elements 11 and 12 fromentering any light-receiving element 12. Each slit unit comprises a slitstructure 16 and a frame 17 holding the slit structure 16. It wouldsuffice to use only one slit unit extending along either the array oflight-emitting element 11 or the array of light-receiving elements 12.Furthermore, the slit units may be replaced by plates each having anumber of through holes or by units each comprising parallel thin platesspaced apart by spacers.

As shown in FIG. 30, the slit structure 16 of each slit unit is ahoneycomb structure made of aluminum foil having a thickness of about0.04 mm. Each cell of the honeycomb structure, which defines a slit, hasa depth of about 15 mm and an inter-face width of about 5 mm. Thethickness of the foil and the inter-face width of the cell can be variedif necessary. The depth of the cell may range from about 5 mm to 30 mm,preferably 10 mm to 20 mm. If the cell depth is too small, the slit unitwill fail to prevent the light emitted from each element 11 fromscattering or the light reflected from any object between the arrays ofelements 11 and 12 from reaching any light-receiving element 12. If thecell depth is too large, the sensor 10 will be too large.

A method of manufacturing either slit unit will be described, withreference to FIGS. 31A to 31E.

First, as shown in FIG. 31A, a honeycomb structure made of aluminumfoil, 700 mm long and 100 mm high, composed of cells about 15 mm deep.The structure is coated with mat black paint or the like, so as not toreflect or scatter light. Next, as shown in FIG. 31B, the honeycombstructure is compressed between two flat plates, while being pulled atboth ends. Unless the structure is pulled, the cells will not becompressed uniformly in some case. As a result, a compressed structureshown in FIG. 31C is obtained. Then, cell layers are peeled off as shownin FIG. 31C, thereby reducing the number of cell layers to a desiredvalue. Finally, as shown in FIG. 31D, the compressed honeycomb structureis pulled into the gap between two parallel plates, while being pulledat both ends. The resultant structure is cut at both ends, forming aslit unit which has a desired length.

As is shown in FIG. 32, the two identical slit structures 16 havingdistance H1 and H2 between the object and the sensor, and depths X1 andX4 are spaced apart for a distance (X2+X3). On the basis of thesedimensional values H1, H2, X1, and X2, slit diameters Y1 and Y2 (i.e.,inter-face widths) are determined for the slit structures 16,respectively. The depths X1 and X4 and the slit diameters Y1 and Y2 canbe set at any values desirable. The number of cell layers forming eachslit structure 16 can be varied. In addition, the slit structure 16 caneasily be coated with mat paint.

A second example of the sensor 10 will be described, with reference toFIGS. 33A and 33B. FIGS. 33A and 33B are a sectional view and aperspective view, respectively, both schematically showing the sensor.

As shown in FIG. 33A, this sensor comprises light-emitting elements 11for emitting near infrared beams having a wavelength of 940 nm andlight-receiving elements 12 for receiving the near infrared beams. Theelements 11 are arranged on the substrate 22 of a light-emission controlcircuit substrate 22, and the elements 12 on the substrate 24 of alight-reception control circuit. The elements 11 are spaced apart fromone another at intervals of 10 mm. Similarly, the elements 12 are spacedapart from one another at intervals of 10 mm. Each light-receivingelement 12 opposes the associated light-emitting element 11, spacedapart therefrom for a distance of 800 mm, for detecting any objectlocated between it and the associated light-emitting element 11. Thesensor further comprises two slit units of the type shown in FIG. 29.The slit units are arranged between the array of light-emitting elements11 and that of light-receiving elements 12, extending along thesearrays, respectively. They prevent the light emitted from elements 11from scattering to a reflector 70 extending along them and prevent thelight reflected by the reflector 70 from reaching the light-receivingelement 12.

As shown in FIG. 33B, an array composed of n light-emitting elements 11extends along the X axis, and an array composed of n light-receivingelements 12 extends parallel to the array of elements 11 such that theelements 12 oppose the elements 11, respectively. Two slit units 18,each comprising a slit structure 16 and a frame 17, are arranged infront of these arrays, respectively. The n optical axes, each extendingbetween one light-emitting element 11 and the associated light-receivingelement 12, lie in an X-Y plane, extending parallel along the Y axis.The reflector 70 lies in a plane parallel to the X-Y plane, as well.Hence, the sensor can detect any object existing in the X-Y plane ormoving thereto.

Since the slit units 18, each having a honeycomb structure, can easilybe manufactured by the method explained with reference to FIGS. 31A to31E, it is easy to manufacture the second example of the sensor 10.

FIG. 34 is a diagram illustrating a third example of the sensor 10. Thissensor comprises an array of light-emitting elements 11 and an array oflight-emitting elements 12. The array of elements 11 is mounted on alight emission control circuit board 22, and the array of elements 12 ona light reception control circuit board 24. These arrays are spacedapart by 800 mm, extending parallel to each other and to the plane ofthe drawing. The light-emitting elements 11 are arranged at intervals of15 mm, for emitting near infrared beams having a wavelength of 940 nm.The light-receiving elements 12 are arranged at intervals of 15 mm andoppose the light-emitting elements 11, respectively, for receiving thenear infrared beams emitted from the associated elements 11. A honeycombslit structure 16 is arranged in front of each light-emitting element11, for preventing the near infrared beam emitted by the element 11 fromscattering. Similarly, a honeycomb slit structure 16 is arranged infront of each light-receiving element 12, for preventing any light beamreflected or scattered from a reflector lying in a plane parallel to theplane of the drawing.

FIG. 35 shows a fourth example of the sensor 10. The fourth example hasno honeycomb slit structures. Despite this, it can detect any objectexisting between an array of light-emitting elements 11₁ to 11_(N) andan array of light-receiving elements 12₁ to 12_(N), not influenced bylight beams reflected or scattered from a reflector 70. As in the secondexample shown in FIG. 33B, the light-emitting elements 11₁ to 11_(N) arearranged in an X-Y plane, spaced apart at regular intervals, and thelight-receiving elements 12 are also arranged in the X-Y plane, spacedapart at regular intervals and opposing the light-emitting elements 11₁to 11_(N), respectively.

The fourth example of the sensor 10 operates in the following steps:

a. First, the light-emitting element 11₁ emits beams, and the first twolight-receiving elements 12₁ and 12₂ receive the beams as indicated bybroken lines 81 in FIG. 35.

b. Then, the second light-emitting element 11₂ emits beams, and thefirst three light-receiving elements 12₁, 12₂ and 12₃ receive the beamsas indicated by solid lines 82 in FIG. 35.

c. Next, the third light-emitting element 11₃ emits beams, and thesecond, third and fourth light-receiving elements 12₂, 12₃ and 12₄receive the beams.

d. Further, any Mth light-emitting element (3<M<N) to emit beams, andsaid (M-1)th, Mth and (M+1)th light-receiving elements receive thebeams; and

e. Finally, the last light-emitting element 11_(N) emits beams, and thelast two light-receiving elements 12_(N-1) and 12_(N) receive the beams.

The sequence of steps a to e is repeated at high speed. When at leastone of the light-receiving elements 12₁ to 12_(N) receives no beam atall, it is detected that an object exists between the array oflight-emitting elements and the array of light-receiving elements. Sincethe two or three light-receiving elements can receive a beam emitted byone light-emitting element, substantially at the same time, an objectwhich is smaller than the intervals at which the elements 11₁ to 11_(N)and 12₁ to 12_(N) are spaced apart. Needless to say, the fourth exampleof the sensor 10 may also have honeycomb slit structures as the secondexample shown in FIG. 33B.

Furthermore, the signals the light-receiving elements 12₁ to 12_(N)generate as the sequence of steps a to e is repeated may be stored intoa memory (not shown) and compared with the positions of thelight-receiving elements which are known. In this case, the position ofan object, if existing between the arrays of the light-emitting and-receiving elements, can be determined to the precision of the intervalsat which the light-receiving elements 12₁ to 12_(N) are spaced apart.

Moreover, it is possible to determine whether or not the light-emittingelements and the light-receiving elements are out of order. Morespecifically, the steps a to e are carried out with no object existingbetween the arrays of the elements 11₁ to 11_(N) and 12₁ to 12_(N), thesignals Pon₁ to Pon_(n) which the light-receiving elements 12₁ to 12_(N)generate in the process are stored into the memory. Then, the sequenceof the following steps is performed, with no object existing between thearrays of the elements 11₁ to 11_(N) and 12₁ to 12_(N) :

f. First, all light-emitting elements, except the element 11₁, emitbeams, and the signals Poff₁ generated by the light-receiving elements12₁ and 12₂ are stored into the memory.

g. Next, all light-emitting elements, except the element 11₂, emitbeams, and the signals Poff₂ generated by the light-receiving elements12₁, 12₂ and 12₃ are stored into the memory.

h. Then, all light-emitting elements, except the element 11₃, emitbeams, and the signals Poff₃ generated by the light-receiving elements12₂, 12₃ and 12₄ are stored into the memory.

i. Further, all light-emitting elements, except any Mth light-emittingelement (3<M<N) emit beams, and the signals Poff₄ generated by theelements 12₃, 12₄ and 12₅, the signals Poff_(m) generated by theelements 12_(M-1), 12_(M) and 12_(M+1), are stored into the memory.

j. Finally, all light-emitting elements, but the element 11_(N), emitbeams, and the signals Poff_(n) generated by the light-receivingelements 12_(N-1) and 12_(N) are stored into the memory.

If the signals Pon₁ to Pon_(n) indicate absence of an object, and thesignals Poff₁ to Poff_(n) also indicate absence of an object, it isdetermined that all light-emitting elements and all light-receivingelements operate well.

If the signals Pon₁ to Pon_(n) indicate absence of an object, while thesignals Poff_(m) (1<m<n) indicate presence of an object, it isdetermined that the light-receiving element 12_(M) (1<M<N) cannotperform its function.

If the signals Pon_(m) indicate presence of an object, while the signalsPoff₁ to Poff_(n) indicate absence of an object, it is determined thatthe light-emitting element 11_(M) cannot emit a beam.

If the signals Pon_(m-1), Pon_(m) and Pon_(m+1) indicate presence of anobject, while the signals Poff₁ to Poff_(n) indicate absence of anobject, it is determined that the light-receiving element 12_(M) cannotperform its function.

FIG. 36 illustrates a fifth example of the sensor 10. The fifth examplehas no honeycomb slit structures. Despite this, it can detect any objectexisting between an array of light-emitting elements 11₁ to 11_(N) andan array of light-receiving elements 12₁ to 12_(N), not influenced bylight beams reflected or scattered from a reflector 70. As in the fourthexample shown in FIG. 35, the fifth example comprises an array 71 ofelements and an array 72 of elements, which are arranged in an X-Yplane, opposing each other, extending parallel to each other, and spacedapart from each other. The array 71 comprises two light-emittingelements 11₁ and 11₂ located at the ends of the array, respectively, anda plurality of light-receiving elements 12₁ to 12_(M) arranged betweenthe light-emitting elements 11₁ and 11₂. Similarly, the array 72comprises two light-emitting elements 11₃ and 11₄ located at the ends ofthe array, respectively, and a plurality of light-receiving elements 12₁' to 12_(M) ' arranged between the light-emitting elements 11₁ and 11₂.

The fifth example of the sensor 10 operates in the following steps:

a. First, the light-emitting element 11₁ emits beams, and thelight-receiving elements 12₁ ' to 12_(M) ' simultaneously receive thebeams as indicated by broken lines 83 in FIG. 36.

b. Then, the light-emitting element 11₂ emits beams, and thelight-receiving elements 12₁ ' to 12_(M) ' simultaneously receive thebeams as indicated by broken lines 84 in FIG. 36.

c. Next, the light-emitting element 11₃ emits beams, and thelight-receiving elements 12₁ to 12_(M) simultaneously receive the beamsas indicated by solid lines 85 in FIG. 36.

d. Further, the light-emitting element 11₄ emits beams, and thelight-receiving elements 12₁ to 12_(M) simultaneously receive the beamsas indicated by solid lines 86 in FIG. 36.

The sequence of steps a to d is repeated at high speed, whereby anobject, if any between the arrays 71 and 72, can be detected. Since aplurality of light-receiving elements 12₁ to 12_(M) or a plurality oflight-emitting elements 12₁ ' to 12_(M) ' receives beams at the sametime, an object which is smaller than the intervals at which thelight-receiving elements are spaced apart. It is desirable that thefifth example of the sensor 10 have honeycomb slit structures as thesecond example (FIG. 33B). If provided with honeycomb slit structures,the beams emitted from any light-emitting element can be directed atbroader angles to the light-receiving elements. Needless to say, thefifth example of the sensor 10 can operate well if it has five or morelight-emitting elements, instead of four, provided that at least onelight-emitting member is located at each end of either array.

FIG. 37 shows a sixth example of the sensor 10. The sixth example has nohoneycomb slit structures. Despite this, it can detect any objectexisting between an array of light-emitting elements 11₁ to 11_(N) andan array of light-receiving elements 12₁ to 12_(N), not influenced bylight beams reflected or scattered from a reflector 70. As shown in FIG.37, the sixth example comprises an array 73 of elements and an array 74of elements, which are arranged in an X-Y plane, opposing each other,extending parallel to each other, and spaced apart from each other. Thearray 73 comprises two light-receiving elements 12₁ and 12₂ located atthe ends of the array, respectively, and a plurality of light-emittingelements 11₁ to 11_(M) arranged between the light-emitting elements 12₁and 12₂. Similarly, the array 72 comprises two light-receiving elements12₃ and 12₄ located at the ends of the array, respectively, and aplurality of light-emitting elements 11₁ ' to 11_(M) ' arranged betweenthe light-receiving elements 12₁ and 12₂.

The sixth example of the sensor 10 operates in the following steps:

a. First, the light-emitting elements 11₁ to 11_(M) are sequentiallyoperated, emitting beams toward the light-receiving element 12₃, and theelement 12₃ receives these beams at the same time as indicated by thesolid lines 88 in FIG. 37.

b. Next, the light-emitting elements 11₁ to 11_(M) are sequentiallyoperated again, emitting beams toward the light-receiving element 12₄,and the element 12₄ receives these beams at the same time as indicatedby the solid lines 88 in FIG. 37.

c. Then, the light-emitting elements 11₁ ' to 11_(M) ' are sequentiallyoperated, emitting beams toward the light-receiving element 12₁, and theelement 12₁ receives these beams at the same time as indicated by thebroken lines 87 in FIG. 37.

d. Finally, the light-emitting elements 11₁ ' to 11_(M) ' aresequentially operated again, emitting beams toward the light-receivingelement 12₂, and the element 12₂ receives these beams at the same timeas indicated by the broken lines 87 in FIG. 37.

The sequence of steps a to d is repeated at high speed, whereby anobject, if any between the arrays 73 and 74, can be detected. Since aplurality of light-emitting elements 11₁ to 11_(M) or a plurality oflight-emitting elements 11₁ ' to 11_(M) ' emit beams at the same time,an object which is smaller than the intervals at which thelight-receiving elements are spaced apart. It is desirable that thesixth example of the sensor 10 have honeycomb slit structures as thesecond example (FIG. 33B). If provided with honeycomb slit structures,the beams emitted from any light-emitting element can be directed atbroader angles to the light-receiving elements. Needless to say, thesixth example of the sensor 10 can operate well if it has five or morelight-receiving elements, instead of four, provided that at least onelight-receiving member is located at each end of either array.

FIG. 38 illustrates a scintillation camera according to the presentinvention, which has a sensor of the type shown in FIGS. 33A and 33B.

As shown in FIG. 38, this scintillation camera further comprises adetector 48 having a detection surface 49 which is a reflector 70. Thesensor comprises an array of n light-emitting elements 11 and an arrayof n light-receiving elements 12. These arrays are attached to theopposing sides of the detector 48. Although not shown in FIG. 38, twoslit units 18, each comprising a slit structure 16 and a frame 17, arearranged in front of the arrays, respectively. The n light-emittingelements 11 oppose the n light-receiving elements 12, respectively, eachfor emitting a beam to the associated light-receiving element 12 alongan optical axis 13. The elements 11 and the elements 12 protrude suchthat the n optical axes 13 lie in a horizontal plane 20 mm above thedetection surface 49 of the detector 48. Hence, the sensor can detectany object at a distance equal to or less than 20 mm from the detectionsurface 49--not affected by light beams reflected or scattered from thereflector 70 (i.e., the detection surface 49 of the detector 48).

Thanks to the use of the non-contact type sensor, the detector 48 can beheld at a predetermined distance from the body surface of a subjectwhile being rotated in an orbit around the subject to acquire SPECT datatherefrom. Also the detector 48 can be moved along the ridge line of thesubject in order to acquire data required for forming a whole-body imageof the subject. Thus, it is unnecessary to store in a memory the datarepresenting the desired orbit or the data representing the desiredorbit is not stored in the memory. The time for acquiring the SPECT datafrom a subject can be shorter than otherwise, whereby the throughputincreases and the operator's toil is lessened, and the reliability ofthe scintillation camera is enhanced. Since the detector 48 can approachthe bed and far therefrom, such that it remains always at apredetermined distance from the body surface of a subject, the imageresolution of the camera is high. Two identical non-contact sensors ofthe type shown in FIG. 38 may be used, with a subject located betweenthem, during the acquisition of the SPECT data, to thereby detect thebody axis of the subject. This helps provide high-quality tomographicimages of the subject.

The non-contact type sensor according to the present invention can beemployed in combination with an X-ray diagnostic apparatus, instead of ascintillation camera used as a nuclear medicine diagnostic apparatus.

Some of the embodiments described above are designed to achievewhole-body data acquisition, whereas the other embodiments are designedto perform SPECT data acquisition. The present invention is not limitedto these two types; it is applied to a scintillation camera which canperform both whole-body data acquisition and SPECT data acquisition, oneafter the other without a break. For instance, SPECT data acquisitionmay be started upon completion of whole-body data acquisition. In thiscase, the data showing a whole-body data acquisition start position anda SPECT data acquisition start position and the data specifying thesetypes of data acquisition are input, and both types of data acquisitionare started thereafter. Since the whole-body data acquisition and theSPECT data acquisition are sequentially effected in the order mentioned,without any break, the entire data acquisition time is shorter thanotherwise.

In the embodiments of scintillation camera, described above, thedetector 48 is horizontally moved, while remaining at the 0° position(FIG. 11), or is rotated around the subject, while not movinghorizontally at all. According to the present invention, the detector 48may be moved horizontally, while being rotated around the subject, asillustrated in FIG. 39. In this instance, the detector 48 is moved in ahelical path, thus accomplishing so-called "helical scanning" to acquireSPECT from the subject.

In addition, the present invention can be applied to a scintillationcamera comprising a plurality of detectors and a plurality of sensors,each of which can be housed within one sensor so that the sensor may belocated close to any adjacent detector.

As described above, the detector is maintained at a predetermineddistance from a subject throughout the whole-body data acquisition orthe SPECT data acquisition. Instead, the detector may be moved along aprescribed whole-body data acquisition path or in a prescribed SPECTdata acquisition orbit, and is made to far motion from the subject whenit approaches the subject too much by near motion, and return to theprescribed path or orbit upon faring a predetermined distance from thesubject or upon elapse of a predetermined period from the start of farmotion.

In the above-described embodiments, the light-emitting and -receivingelements are located such that the optical axes they define lie in oneplane. When any part of the subject interfere one or more of the opticalaxes, the detector 48 is made to far motion from the subject. Sometimesit is desirable that the detector 48 be located very near a part of thesubject. On such an occasion, it suffices to render inoperative those ofthe light-emitting and -receiving elements which define optical axes tobe interfered by said part of the subject.

Moreover, it is possible with the present invention to use a contacttype sensor along with the non-contact type sensor. If this is the case,the contact type sensor serves to stop the detector 48 or move the sameaway from the subject the moment the detector 48 comes into contact withthe subject. The use of both a contact type sensor and a non-contacttype sensor can increase the safety of the scintillation camera.Further, a sensor, either a contact type one or a non-contact type one,may precede the detector 48 while moving together with the detector 48,thereby serving to prevent the detector 48 from contacting the subject.This also ensures safety.

In the embodiment described above, it is desirable that thelight-emitting elements be infrared ray emitting ones, laser-beamemitting diodes, or the like.

Further, to achieve whole-body data acquisition, the subject may bescanned from the toe to the vertex, not vice versa as in some of theembodiments described above.

The above embodiments of the scintillation camera which has twodetectors may be modified into one which has only one detector. In sucha modification, it suffices to attach the sensor holders 26 to theopposing sides of the single detector, respectively, and to mount alight-emitting element 11 on the first holder 26 and a light-receivingelement 12 on the second holder 26.

As shown in FIGS. 26A and 26B, the fourth embodiment has two sensorunits each comprising a light-emitting element and a light-receivingelement. Instead, a scintillation camera according to the invention mayhave only one sensor unit or three or more sensor units. Further, thesensor units may be connected to the rear ends of the sensor holders 26,instead of the forward ends thereof as shown in FIG. 25B.

In the above-described embodiments of the scintillation camera accordingto the invention, the bed is stationary, whereas the detector (ordetectors) is movable. Alternatively, the bed may be movable and thedetector is fixed in place.

Moreover, other various changes and modifications can be made, withoutdeparting from the scope and spirit of the present invention.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the present invention in its broaderaspects is not limited to the specific details, representative devices,and illustrated examples shown and described herein. Accordingly,various modifications may be made without departing from the spirit orscope of the general inventive concept as defined by the appended claimsand their equivalents.

What is claimed is:
 1. A scintillation camera designed to form atomographic image of a subject from radiation emitted from radioisotopeadministrated to the subject, said camera comprising:data acquiringmeans for acquiring data required to reconstract a tomographic image ofthe subject, having a gamma-ray detector; a sensor circuit forgenerating ON/OFF signal which corresponds to distance between thegamma-ray detector and the subject, based in a output of a sensor;moving means for moving said gamma-ray detector toward and away from thesubject in accordance with the ON/OFF state detected by said sensorcircuit; recording means for recording positions of the gamma-raydetector in accordance with the ON/OFF state detected by said sensorcircuit; means for obtaining a ridge line of the subject from thepositions of said gamma-ray detector recorded by said recording means.2. A scintillation camera according to claim 1, wherein said holdingmeans further comprises a contact sensor for detecting a mutual contactof said detecting means and the subject.
 3. A scintillation cameraaccording to claim 1, wherein said sensor is an ultrasonic sensor fordetecting the distance between the subject and said detecting means byusing ultrasonic waves.
 4. A scintillation camera according to claim 1,wherein said sensor is a reflection-type optical sensor for detectingthe distance between the subject and said detecting means by emittinglight to the subject and receiving the light reflected therefrom.
 5. Ascintillation camera according to claim 1, wherein said sensor is atension sensor comprising a strip of cloth stretched in the same planeat a predetermined tension, for detecting the distance between saidsubject and said detecting means in accordance with changes in thetension.
 6. A scintillation camera according to claim 1, wherein saidsensor is a counter-type optical sensor comprising an array oflight-emitting elements and an array of light-receiving elementsopposing said array of light-emitting elements, respectively, fordetecting the distance between said subject and said detecting means inaccordance with signals which said array of light-receiving elementsgenerate as said subject moves in a space between said array oflight-emitting elements and said array of light-receiving elements.
 7. Ascintillation camera according to claim 1, further comprising means forhousing said sensor when said sensor is out of use.
 8. A scintillationcamera according to claim 1, wherein said sensor includes:alight-emitting element; a light-receiving element opposing saidlight-emitting element, spaced apart therefrom by a predetermineddistance, and located in the same plane as said light-emitting element;and a slit unit located in front of at least one of said light-emittingelement and said light-receiving element.
 9. A scintillation cameraaccording to claim 1, wherein said sensor includes:an array oflight-emitting elements; an array of light-receiving elements opposingsaid array of light-emitting elements, respectively, spaced aparttherefrom by a predetermined distance, and located in the same plane assaid array of light-emitting elements; a slit unit located in front ofthe elements of at least one of said array of light-emitting elementsand said array of light-receiving elements; and means for preventing atleast one element of said array of light-emitting elements from emittinga beam, and at least one element of said array of light-receivingelements from receiving a beam.
 10. A scintillation camera according toclaim 1, wherein said sensor includes:an array of light-emittingelements for emitting beams; an array of light-receiving elementsopposing said array of light-emitting elements, spaced apart therefromby a predetermined distance, and arranged in the same plane as saidarray of light-emitting elements, for receiving the beams emitted fromsaid array of light-emitting elements; and means for applying the beamemitted from each light-emitting element sequentially to saidlight-receiving elements, repeatedly a number of times which is anintegral multiple of the number of said light-emitting elements.
 11. Ascintillation camera according to claim 1, wherein said sensorincludes:two parallel arrays of light-emitting elements; at least twolight-receiving elements located at the ends of each of said arrays oflight-emitting elements; and means for repeatedly applying the beamssequentially emitted from the light-emitting element of one of saidarray to each of at least two light-receiving elements located at theends of the other array.
 12. A scintillation camera according to claim1, wherein said sensor includes:an array of first to Nth light-emittingelements; an array of first to Nth light-receiving elements opposingsaid first to Nth light-emitting elements, respectively, spaced aparttherefrom by a predetermined distance, and located in the same plane assaid first to Nth light-emitting elements; means for repeating the stepsof: causing the first light-emitting element to emit beams and the firstand second light-receiving elements to receive the beams and generatesignals; causing the second light-emitting element to emit beams and thefirst, second and third light-receiving elements to receive the beamsand generate signals; causing any Mth light-emitting element (1<M<N) toemit beams and the (M-1)th, Mth and (M+1)th light-receiving elements toreceive the beams and generate signals; and causing the Nthlight-emitting element to emit beams and the (N-1)th and Nthlight-receiving elements to receive the beams and generate signals; andmeans for recording the beams emitted by said first to Nthlight-emitting elements and the signals generated by said first to Nthlight-receiving elements, checking the beams and signals against thepositions of said first to Nth light-emitting elements and the positionsof said first to Nth light-receiving elements, thereby detecting aposition of a subject existing between said array of first to Nthlight-emitting elements and said array of first to Nth light-receivingelements.
 13. A scintillation camera according to claim 1, wherein saidsensor includes:an array of first to Nth light-emitting elements; anarray of first to Nth light-receiving elements opposing said first toNth light-emitting elements, respectively, spaced apart therefrom by apredetermined distance, and located in the same plane as said first toNth light-emitting elements; and means for performing a first sequenceof steps and a second sequence of steps when no object exists betweensaid array of first to Nth light-emitting elements and said array offirst to Nth light-receiving elements; said first sequence of stepsconsisting of the steps of: causing the first light-emitting element toemit beams and the first and second light-receiving elements to receivethe beams and generate signals; causing the second light-emittingelement to emit beams and the first, second and third light-receivingelements to receive the beams and generate signals; causing any Mthlight-emitting element (1<M<N) to emit beams and the (M-1)th, Mth and(M+1)th light-receiving elements to receive the beams and generatesignals; and causing the Nth light-emitting element to emit beams andthe (N-1)th and Nth light-receiving elements to receive the beams andgenerate signals; and said second sequence of steps consisting of thesteps of: causing the first light-emitting element not to emit beams andthe first and second light-receiving elements to generate signals;causing the second light-emitting element not to emit beams and thefirst, second and third light-receiving elements to generate signals;causing any Mth light-emitting element (1<M<N) not to emit beams and the(M-1)th, Mth and (M+1)th light-receiving elements to generate signals;and causing the Nth light-emitting element not to emit beams and the(N-1)th and Nth light-receiving elements to generate signals.
 14. Ascintillation camera according to claim 1, wherein said sensor is atension sensor comprising a plurality of strings stretched in the sameplane at a predetermined tension, for detecting the distance betweensaid subject and said detecting means in accordance with changes in thetension.